1. Field of the Invention
The present invention relates to a grinding method of and a grinding machine for grinding a workpiece with a rotating grinding wheel wherein grinding fluid is reliably led to the grinding point.
2. Description of the Related Art
Conventionally, there have been used some kinds of grinding machines, for example as shown in FIGS. 10 and 11, in which a grinding wheel G rotates at a high speed for higher grinding efficiency. In these grinding machines, although an air layer flows along and around the grinding wheel G, the air so flowing must be cut off in order to ensure that the grinding fluid reliably led to a grinding point where a workpiece W is ground with the grinding wheel G. FIG. 10 shows a first conventional grinding machine wherein the grinding fluid is pressurized and ejected to the grinding point from a nozzle 40 at such a high speed that the air layer can be cut off to lead the grinding wheel to the grinding point reliably. FIG. 11 shows a second conventional grinding machine wherein the spout of a nozzle 41 faces to the circumferential surface of the grinding wheel G at the right angle. Therefore, the grinding fluid is perpendicularly ejected against the circumferential surface of the grinding wheel G so that the air layer flowing around the grinding wheel can be cut off to lead the grinding fluid to the grinding point reliably.
The inventors of the present invention found out that the air flow flows faster at axial end portions on the circumferential surface of the grinding wheel G than at the middle thereof. This is because air layers of flowing air on both lateral sides of the grinding wheel G are spirally and acceleratively drown in the rotational direction by its rotation from the rotational center to the circumferential surface and thus affect the air flows at the axial end portions of the circumferential surface. This makes the cause to partly obstruct leading the grinding fluid to the grinding point. Especially, where the peripheral velocity of the grinding wheel G is increased to high speeds such as 120 m/s or more for high grinding efficiency, or where the thickness of the grinding wheel G is thin, the foregoing drawback occurs remarkably. In these cases, it becomes hard to lead the grinding fluid to the grinding point reliably. In the second conventional grinding machine, the grinding fluid ejected from the nozzle 41 is able to cut off the air flow on the circumferential surface of the grinding wheel G and is put thereto to be led to the grinding point. However, since the air flows on both lateral sides of the grinding wheel G affect those at the axial end portions of the circumferential surface, the grinding fluid is hardly put on the circumferential surface and whereby it does not reach the grinding point. In the first conventional grinding machine, since the grinding fluid is pressurized for being led to the grinding point, there must be consumed much volume of the grinding fluid. Accordingly, there must be used a high pressure pump and a large tank for the grinding fluid, whereby the facility must be of high cost. In addition, the grinding fluid and electric power are increased in consumption which causes the maintenance cost to increase.